Spirochetes

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Spirochaetales
Systematics
Domain : Bacteria (bacteria)
Department : Spirochaetae
Class : Spirochetes
Order : Spirochaetales
Scientific name of the  department
Spirochaetae
Cavalier-Smith 2002
Scientific name of the  class
Spirochaetes
Cavalier-Smith 2002
Scientific name of the  order
Spirochaetales
Buchanan 1917
Familys

Spirochetes are a group of gram-negative , helical, actively moving bacteria that are characterized by a characteristic musculoskeletal system (see below). As pathogens , some cause what are known as spirochetoses (spirochete diseases ). The order Spirochaetales represents the only order in the class Spirochaetes , which in turn forms the only class in the division (phylum) Spirochaetae . The order includes four families , according to new phylogenetic studies from 2013 it was suggested that the families should be elevated to the rank of an order because of their clear differences.

features

In contrast to the also helical (helical) spirils , spirochetes do not have a rigid shape given by the cell wall , but flexible and pliable bodies. They do not possess as other flagellated bacteria outwardly projecting flagella (flagella), but so-called endoflagella (see below). Spirochetes are also characterized by their very small diameter in relation to their length. The very characteristic shape of the spirochetes corresponds to a comparatively homogeneous genome in all members of this group. Spirochetes do not form spores .

As a special feature, they have tubulin- like proteins , which suggests an origin of these structures, which occur almost exclusively in eukaryotes, in prokaryotic bacteria.

The cell ends are generally not bent into a hook shape, this is typical only for members of the Leptospiraceae family. In Brachyspiraceae and Spirochaetaceae, the murein layer in the cell wall contains the diamino acid L - ornithine as a diagnostically important amino acid . In the Leptospiraceae, diaminopimelic acid takes over this function. It is not yet clear which diamino acid occurs in the Brevinemataceae.

In terms of physiological properties, the spirochetes are very heterogeneous. Some of the bacterial species are strictly anaerobic , others facultatively anaerobic, and microaerophilic species are also known. They all carry out a chemoorgano-heterotrophic metabolism , but differ in the substrates that they can utilize. Brevinemataceae and Spirochaetaceae use carbohydrates and / or amino acids for this , Brachyspiraceae can use amino sugars in addition to mono- , di- and trisaccharides . Leptospiraceae, on the other hand, are dependent on fatty acids and fatty alcohols .

Cell structure and modes of movement

Figure 2: Schematic representation of a spirochete

Spirochetes differ from other bacteria in their particular structure and movement (Fig. 2). They have a flexible, elongated body in contrast to most other bacteria, which have an elastic shape predetermined by their cell wall. They have one or more flagella at each end (red in the picture). Unlike other bacteria, these are not turned away from the body, but facing each other. The flagella of each cell end usually overlap in the middle and together form a bundle that extends from one cell end to the other, the so-called axial filament. The flexible spirochete body (also known as the “protoplasmic cylinder”) is wound in a helical shape around this bundle. The whole, the body and the flagella bundle, are surrounded by a shell (blue in the picture). This is why this type of flagella is also known as endoflagella .

Image 3: Schematic representation of a spirochete in cross section: Outer membrane = outer membrane , protoplasm = cytoplasm , flagella = flagellum , peptidoglycan = peptidoglycan, inner membrane = inner membrane, i.e. H. the cell membrane

In the cross-section (Fig. 3) it can be seen that the flagella lie in an area between the inner membrane, which surrounds the cytoplasm , and the outer membrane. In the more recent specialist literature, the term periplasmic flagella is therefore used. The order and number of the periplasmic flagella varies in the different species. Some species have only one flagellum, other species, e.g. B. from Cristispira up to 100 flagella. In representatives of the families of the Brachyspiraceae, Brevinemataceae and Spirochaetaceae, the flagella overlap in the middle of the cell, this is not the case with the Leptospiraceae.

It is believed that the spirochetes move by rotating the flagella around their axis by means of their basal apparatus, as in other flagellated bacteria. As a result, friction causes the entire body to rotate , which in a sense screws itself through the surrounding medium, like a corkscrew through a cork. This mode of movement allows the spirochetes to move through highly viscous media, in which other flagellated bacteria, in which their helical flagella protruding into the medium function like propellers, cannot move. Spirochetes can enter the body of a living being through mucus and cell tissue, which is important for the pathogenic representatives. They can also move in nutrient media that contain 1% agar and are therefore considered to be solid nutrient media. However, they can not move as quickly as other bacteria in normal viscous media.

In addition to the described mode of movement, screwing through the medium, they can also move by snaking. It can be assumed that this meandering is due to the fact that the endoflagella in the bundle move longitudinally against each other, but the mechanism of this movement is still largely unexplained. The ends of some spirochetes are curved like a hook. It is not clear whether this is used for movement, like a propeller.

However, there are also coccoid (spherical) spirochetes that can only be assigned to spirochetes by means of phylogeny .

Occurrence

In terms of habitat , the group of these microorganisms is very heterogeneous. They occur in soils , bodies of water and water sludge as well as harmless commensals or parasites in the intestines of molluscs and insects as well as in the gastrointestinal tract and throat of mammals. In mammals, they can also appear as kidney parasites.

Systematics

The spirochetes are isolated in the bacterial family tree . This is confirmed by their unusual cell structure. The Spirochaetae form their own phylum (a division , in the systematics of bacteria also referred to as Divisio ), with only one class Spirochaetes and one order Spirochaetales. This order consists of four families ; this overview also shows the associated type genera (as of 2014):

According to new phylogenetic studies from 2013 by Gupta et al. a. It was proposed to the representatives of these spirochete families to raise the families to the rank of an order because of their clear differences (see also the proposal for a modified systematics of the Spirochaetaceae ). The suggested names for it are Brachyspiriales, Brevinematales, Leptospiriales and Spirochaetales. It was also proposed to assign the genera Borrelia and Cristispira to the newly established family of Borreliaceae. According to this proposal, this family is in the order Spirochaetales. Such changes are usually only recognized with the new edition of the important reference work on the phylogenetic systematics of bacteria, Bergey's Manual of Systematic Bacteriology .

Species dangerous to humans

Spirochete diseases that are significant for humans are leptospiroses ( Weil's disease , field or harvest fever and other leptospiroses), relapsing fever and the rat-bite disease sodoku . Although most species of spirochete are harmless to humans, there are some representatives that are considered to be dangerous pathogens. So is Treponema pallidum the causative agent of syphilis and Treponema pertenue the causative agent of yaws . Pathogenic species can also be found among the Borrelia: lice relapse fever is caused by Borrelia recurrentis , tick relapse fever is caused by Borrelia duttoni and others and Lyme borreliosis (tick borreliosis ) is caused by Borrelia burgdorferi . The leptospira cause various leptospiroses , the pathogens are mostly transmitted by pets or rats.

The spirochetes can be transmitted to humans through lesions of the skin or mucous membrane (for example through sexual contact ) or through bites from ticks and lice .

Brachyspira pilosicoli has been known as a human colon pathogen since 2018, which is responsible for chronically intermittent watery diarrea. The spread to the liver, spleen, blood and possibly other mucin-secreting organs has yet to be investigated.

literature

  • Curt Magerstedt: A contribution to the morphology of the syphilis pirochetes. In: Arch. Dermatol. Syph. , Volume 185, 1943/44, pp. 272-280.
  • Gerd B. Roemer: The family of the Spirochaetaceae-Spirochätosen. In: Heinz Reploh, Hans Jürgen Otte: Textbook of Medical Microbiology. Edited by Henning Brandis and Hans Jürgen Otte. 5th, revised edition. Stuttgart / New York 1984.

Web links

Commons : Spirochaetes ( Spirochaetes )  - Collection of images, videos and audio files

Individual evidence

  1. ↑ a b c d e f Bruce J. Paster u. a .: Order Spirochaetales . In: Noel R. Krieg u. a. (Ed.): Bergey's Manual of Systematic Bacteriology . 2nd edition, Volume 4: The Bacteroidetes, Spirochaetes, Tenericutes (Mollicutes), Acidobacteria, Fibrobacteres, Fusobacteria, Dictyoglomi, Gemmatimonadetes, Lentisphaerae, Verrucomicrobia, Chlamydiae, and Planctomycetes . Springer, New York 2010, ISBN 978-0-387-95042-6 , pp. 471-501 .
  2. ↑ S. Dröge, J. Fröhlich, R. Radek, H. König: Spirochaeta coccoides sp. nov., a novel coccoid spirochete from the hindgut of the termite Neotermes castaneus . In: Applied and Environmental Microbiology . Vol. 72, 2006, pp. 392-397, PMID 16391069 .
  3. ^ Jean Euzéby, Aidan C. Parte: Taxa above the rank of class: Spirochaetae. In: List of Prokaryotic names with Standing in Nomenclature ( LPSN ). Retrieved August 1, 2014 .
  4. ^ Jean Euzéby, Aidan C. Parte: Class Spirochaetes. In: List of Prokaryotic names with Standing in Nomenclature ( LPSN ). Retrieved August 1, 2014 .
  5. ^ A b Jean Euzéby, Aidan C. Parte: Order Spirochaetales. In: List of Prokaryotic names with Standing in Nomenclature ( LPSN ). Retrieved August 1, 2014 .
  6. ↑ Radhey S. Gupta, Sharmeen Mahmood, Mobolaji Adeolu: A Phylogenomic and Molecular Signature Based Approach for Characterization of the Phylum Spirochaetes and its Major Clades: Proposal for a Taxonomic Revision of the Phylum. In: Frontiers in Microbiology. Volume 4, No. 217, July 29, 2013, ISSN  1664-302X , doi: 10.3389 / fmicb.2013.00217 .
  7. ↑ Karl Wurm, AM Walter: Infectious Diseases. In: Ludwig Heilmeyer (ed.): Textbook of internal medicine. Springer-Verlag, Berlin / Göttingen / Heidelberg 1955; 2nd edition, ibid. 1961, pp. 9-223, here: pp. 148-154.
  8. ↑ The spirochete Brachyspira pilosicoli, Enteric Pathogen of Animals and Humans . PMID 29187397 , Colon Pathogen
  9. ↑ The spirochete Brachyspira pilosicoli, Enteric Pathogen of Animals and Humans . PMID 19833772 , Mucin